Tomato peeling by ohmic heating: Effects of lye-salt combinations and post-treatments on weight loss,peeling quality and firmness

Ohmic heating without lye has shown promise in tomato peeling; however the use of lye is known to yield high peeled-product quality. This investigation was aimed at determining whether a combination of ohmic heating and low lye concentrations could be synergistic. The results indicated that 0.01/0.5% NaCl/KOH at 2020 V/m was the best condition for tomato peeling in terms of quality, weight loss, and peel cracking time. Further, the treatment showed weight loss that was not significantly different from conventional lye peeling at 7% NaOH and 7% KOH (p < 0.05). NaCl/NaOH mixtures also showed good results, but the quality of products was lower than that using the same concentration, but a higher field strength with NaCl/KOH mixtures. However, no improvement was found using NaCl/CaCl₂ and NaCl/NaOH/CaCl₂ mixtures which were also found difficult to use due to turbidity and cleaning difficulties. A post-peeling treatment by ohmic heating was investigated to improve firmness of ohmically peeled tomatoes. It was found that the best conditions were 2% CaCl₂ solution at a field strength of 403 V/m for 1 and 5 min, and 484 V/m for 5 min.Industrial RelevanceOur earlier work had shown that ohmic heating resulted in peeling of tomatoes that were immersed in salt solutions. The current work details the impact of using small concentrations of lye (either sodium or potassium hydroxide) on peeling loss and quality. Also, we investigate the potential use of calcium chloride, both as peeling solution or as a post-peeling infusion as it impacts firmness of tomatoes. We show that there are ranges of operating conditions which provide yield and quality comparable to conventional lye peeling at far lower lye concentrations, resulting in potentially significant environmental benefit to companies currently using lye peeling.     

USE of ORGANIC SOLVENTS FOR IMPROVING PEELABILITY of TOMATOES

A prepeeling dip was used to demonstrate that removal or modification of the cuticular waxes from the tomato fruit could be used to improve the tomato peeling process. the tomatoes were dipped at various temperatures for I min prior to regular lye peeling. the optimum temperature was found to be 45C. Several organic solvents including chloroform, ethyl acetate, ketones, and alcohols were used. These tomatoes were compared to tomatoes peeled using the lye without the dip. the prepeeling dip reduced the thickness of the cuticular wax layer and produced cracks in the cutin surface. This facilitated good penetration of lye into the tomato resulting in more complete peeling. Peeling after pretreatment produced 86% well peeled tomatoes as compared to 33% well peeled in the control run.     

Conventional and novel peeling methods for fruits and vegetables: A review

This review explores the effects of various peeling technologies on the peeling performance of fruits and vegetables and peeled product quality. The peeling methods include conventional peeling approaches using hot-water, steam and lye and novel peeling techniques employing infrared radiation heating, ohmic heating and power ultrasound. The working principles, technology characteristics, the major factors affecting the processing efficacy, and limitations of conventional and novel peeling approaches are identified and discussed. Infrared radiation heating, ohmic heating and ultrasound-assist peeling methods have been successfully used to the peeling of tomatoes and other fruits and vegetables. The novel technologies can reduce the use of lye and can improve peeling performance and peeled product quality compared to conventional peeling. The process conditions and food properties are the major determinants affecting the processing efficacy. Future research needs are proposed to scaling-up the technology and exploring other technology used for peeling.Industrial relevance: As a key operation in the fruits and vegetables processing industry, peeling not only directly affects product quality, but also influences the processing cost and the management cost of waste generated by peeling. An unsuitable peeling process may result in low peeling efficiency and quality, high water and energy consumption, and high discharge of waste liquid, leading to the decline of economic benefits and environmental issues. The current work provides important information for selecting suitable peeling methods for high quality and safe products.     

Pear peeling using infrared radiation heating technology

Infrared radiation (IR) heating could be a potential alternative peeling method to address the long-term water supply and wastewater disposal issues involved in the conventional lye peeling process of pears. The objective of this study was to investigate the feasibility of IR peeling technology as an environmentally friendly alternative practice to efficiently produce peeled pear products with superior quality and yield. A pilot IR Dry-Peeling System consisting of catalytic IR emitters, roller conveyor, and peeler remover was developed and used for this research. Effects of the pear firmness and heating time on the peeling performance and product quality were studied. Under the continuous loading condition, the most desirable peeling result was achieved for Bartlett pears in the initial firmness range of 22 to 31 N after 99 s of IR heating. The results of IR peeling indicated superior product quality with relative thin cooking ring (0.76 ± 0.20 mm), limited peeling loss (9.25 ± 1.25%), and fairly ease of peeling (5.33 ± 1.00). According to SEM photomicrographs of pericarp cross-section, IR heating caused loss of integrity and compartmentalization of cells of the hypodermal layer to only “ripe” pears (firmness of 26.5 ± 2.8 N). Thermal effect of IR heating dramatically disrupted the middle lamella of hypodermal cells and resulted in mechanical failure of those cells and subsequent layer loosening of “ripe” pears.     

PEELABILITY AND YIELD OF PROCESSING TOMATOES BY STEAM OR LYE

Approximately 25% of the processed tomatoes grown in California are made into value‐added foods such as whole peeled and diced tomatoes. Peel removal is the first step in this process, and it must be optimized for both quality and yield. The effect of peeling conditions on tomato cultivars Halley 3155 and Heinz 8892 (H 8892) was evaluated. Considerable texture loss results from peeling; however, firmness was greater for cv. Halley 3155 than for cv. H 8892 regardless of peeling conditions utilized. Peeling under low steam pressures (12 psig) was insufficient to adequately peel either cultivar. While high pressure steam (18 psig) was more efficient at peel removal, increasing vacuum level from 20 in. to 24 in. did not improve peelability of either cultivar. Because cultivar affected peelability and yield, specific tomato cultivars should be evaluated and directed to either paste or whole peeled and diced tomatoes as appropriate.     

Effects of infrared radiation heating on peeling performance and quality attributes of clingstone peaches

Salinity and wastewater disposal problems associated with the conventional wet-lye method for peeling clingstone peaches result in considerable negative environment impacts. The efficacy of using infrared (IR) heating as an alternative method for peach peel removal was investigated to eliminate the use of water and chemicals. Peaches sorted into three size categories were double-sided heated under IR with three emitter gaps for a range of heating times from 90 s to 180 s. Wet-lye peeling was used as a control. Results showed that 180 s IR heating for medium sized peaches under an emitter gap of 90 mm yielded 84 mm²/100 mm² peelability and 90 g/100 g peeling yield, produced peeled products with comparable firmness and color to wet-lye peeled peaches. Surface temperature increased rapidly (> 00 °C) during IR heating whereas the flesh temperature at 16 mm beneath skin remained relatively low (<45 °C). Thermal expansion of cell walls and collapse of cellular layers adjacent to skins were found in IR heated peaches and differed from the micro-structural changes observed in lye heated samples, indicating their mechanistic difference. Promoting uniform and rapid surface heating is essential to further develop IR heating as a non-chemical method for peach peeling.     

Microwave-assisted infrared dry-peeling of beetroot: Peeling performance,product quality,and cell integrity

The use of low power-short time microwave (MW) treatment before infrared (IR) heating could help improve the peeling performance of beetroot. MW-assisted IR peeling (MWIR) and IR peeling of beetroot were investigated and compared with the conventional hot-lye peeling method. Also, the effects of these peeling methods on the quality and microstructure were evaluated. Hot-lye peeling at 95 °C for 40 s and 60 s was used as control. Results showed that MW-assisted IR peeling at power 640 W and heating time 7 min produced samples with the highest peelability (99.4%), lowest peel thickness (0.075 mm), and peel remaining (0.8%), lower peeling loss (4.23 g), and better peeling easiness when compared with lye peeling and IR peeling. IR peeling alone produced samples with the lowest peeling loss (2.87 g) and surface colour change, and the highest vitamin C retention (75.32%) than MW-assisted IR and lye peeling respectively. The product microstructure for the different peeling methods showed cellular distortion as a result of thermal expansion. MW pretreatment shows a promising potential to further develop the IR dry-peeling method, to replace the conventional hot lye chemical peeling.     

Fine physicochemical,structural, rheological and gelling properties of tomato pectin under infrared peeling technique

To protect the pulp quality, the effect of infrared peeling on the physicochemical, structural, rheological, and gelling properties of tomato pectin was investigated using newly developed catalytic infrared peeling equipment and compared with manual, hot-water and lye peeling. Compared to manually peeled pectin, the results showed that hot-water peeling reduced the pectin yield by 13.19% but significantly increased the pectin's Z-average radius of gyration (R_g) and hydrodynamic radius (R_H). And the pectin gel had excessive hardness. Lye peeling reduced the pectin yield by 30.43%, the degree of esterification (DE) by 25.97%, R_H by 7.8 nm and R_g by 2.9 nm. And the pectin gel had the worst water-holding capacity and texture. The yield and DE of pectin (IPP) after infrared peeling only decreased by 3.88% and 0.9%. IPP exhibited moderate physicochemical, structural, rheological, and gelling properties, which was the closest to manually peeled pectin. IPP gel showed steady viscoelasticity and high water-holding capacity (96.71%). Conclusively, the infrared peeling technique can provide better pulp quality and is sustainable.     

不同去皮方法对番茄去皮效果和品质的影响

为优化现有番茄去皮工艺,开发新的去皮方法,以去皮难易程度和质量损失评价去皮效果,比较手工去皮、热水去皮、碱液去皮、功率超声去皮和超声与碱液联用去皮对去皮效果和产品质地、颜色、番茄红素提取率、p H值和可滴定酸含量等品质的影响,并结合扫描电子显微镜观察不同去皮方法果皮微观结构。结果表明,功率超声去皮较传统的热水去皮和碱液去皮,去皮难度小,质量损失少,且产品品质良好,番茄红素含量较高,而超声与碱液联用去皮较其他去皮方法虽去皮难度小,但质量损失过高。扫描电子显微镜观察结果表明,功率超声去皮较热水去皮、碱液去皮对果皮角质层的破坏力更大,可能是超声的空化效应使果皮与果肉更易分离,从而降低去皮损失。因此,功率超声去皮是一种潜在的新型环境友好型去皮方法。     

DEFECTS AND PEELABILITY OF PROCESSING TOMATOES

Peeling is one of the first operations in the manufacture of whole peeled and diced tomatoes, and the peelability of processing tomatoes is significantly affected by the presence of various tomato defects, in particular yellow eye and blossom‐end rot. Tomato maturity also impacts both the percentage of peeled fruit and yield. Immature fruits are typically undercolored and small in size. Sunburned regions on the tomato surface are difficult to peel as well. In this study, we determined the impact of 24 selected tomato defects on tomato peelability and yield of whole peeled tomatoes. There are potential advantages to sorting to remove selected tomato defects early in the process.     

Distribution behaviour of acaricide cyflumetofen in tomato during home canning

The distribution behaviour of cyflumetofen in tomatoes during home canning was studied. The targeted compound cyflumetofen was determined by ultra-performance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS) after each process step, which included washing, peeling, homogenisation, simmering and sterilisation. Results indicated that more cyflumetofen was removed by washing with detergent solution compared with tap water, 2% NaCl solution and 2% CH₃COOH solution. Peeling resulted in 90.2% loss of cyflumetofen and was the most effective step at removing pesticide residues from tomatoes. The processing factors (PFs) of tomato samples after each step were generally less than 1; in particular, the PF of the peeling process for cyflumetofen was 0.28.     

Effect of peeling and heating on carotenoid content and antioxidant activity of tomato and tomato-virgin olive oil systems

The effects of peeling and laboratory- or industrial-scale heating on carotenoid content and radical scavenging activity of tomato and tomato-virgin olive oil mixtures were investigated. A decrease in carotenoid content was detected only after long heating times. Such a decrease was lower for the unpeeled than for the peeled tomatoes. No change, either in lycopene concentration or in the chain-breaking activity of the lipophilic fractions, was observed when both laboratory- and industrial-scale heating treatments were performed on peeled-tomato puree containing 5% virgin olive oil. The aqueous fractions, including high-molecular-weight brown polymers formed as a consequence of heating, were also characterized for color, elementary composition and antioxidant activity.     

PEELING AND THE PHYSICAL AND CHEMICAL PROPERTIES OF KIWI FRUIT

Hand peeling of kiwi fruit has some disadvantages such as difficulty during peeling, increase of loss in weight and nutritional value. Peeling of kiwi fruits with alkali (NaOH) was investigated. Some chemical (acidity, pectin, and chlorophyll) and physical properties (Hunter color value and weight loss) of the fruits were determined after selected alkali peeling methods were used. Peeling methods at 80, 90 or 100C temperatures; in 13, 18 or 23% of NaOH solutions and for 3, 4 or 5 min durations were tested and compared with hand peeling. Weight (fruit tissue) loss in hand peeling was higher than alkali peeling. Peeling with alkali was easier. Nutritional value (ascorbic acid content) of alkali peeled fruits was higher than hand peeled kiwi fruit. Because of less weight loss, better green color and high pectin content the method including 15% of NaOH solution at 95C for 4 min was selected as most advantageous peeling method.     

PEELING OF YAMS FOR PROCESSING

White yam (Dioscorea rotundata) lye or flame peeled were evaluated for quality characteristics and peeling loss in comparison to hand peeling. Lye concentration (15–20% at 98°C with a dipping time 3–5 min) effectively removed the histological peel as the flame method, (flame temperature was 857°C and exposure time was 9 min) with a peeling loss of 4% which was significantly lower than for hand peeling. Fresh yams were more readily peeled by these methods than stored yams. The yams peeled by lye or flame when cooked were quite acceptable as hand peeled yams. The adaptability of these methods for industrial scale up are examined.     

Dry-peeling of Tomato by Infrared Radiative Heating: Part I. Model Development

Infrared (IR) dry-peeling of tomatoes has emerged as a nonchemical alternative to conventional peeling methods using hot lye or steam. Successful peel separation induced by IR radiation requires the delivery of a sufficient amount of thermal energy onto the tomato surface in a very short duration. The objective of this study was to understand the transient heat transfer phenomena during IR dry-peeling by developing a computer simulation model. Modeled tomatoes with realistic shapes and different sizes were employed to predict the temperature distributions on their surface and interior during a typical 60 s IR heating. IR radiation was postulated as a mathematically gray-diffuse radiation problem based on the enclosure theory. Radiation heat transfer model combining heat conduction and convection was solved numerically in COMSOL by using a finite element scheme. Changes of tomato thermal properties and phase change of water inside tomato tissues due to temperature increase were considered in the model to improve the prediction accuracy. The developed model can further be used to study the effects of various engineering parameters on IR heating performance relevant to tomato peeling quality and efficiency. Numerical modeling of the heat transfer mechanism provides in-depth understanding of the rapid surface heating characteristics of IR in the tomato dry-peeling process.     

FREEZE PEELING IMPROVES QUALITY OF TOMATOES

SUMMARY— A process of peeling tomatoes using low temperature-short time freezing was perfected. Liquid nitrogen (BP-196°C was used as the refrigerant for freezing the skin and only a thin layer of cells just beneath the skin. The fruit was immediately thawed, after which the skin was quickly and easily removed from the fruit. Liquid nitrogen-peeled samples were evaluated for loss of peel and trim, as well as lycopene and carotene in the peeling process and these losses compared with samples peeled in boiling water. The losses in peel and trim were reduced by approximately 50%, and significantly less lycopene was lost by nitrogen peeling. The peel and trim of fall tomatoes had a greater amount of lycopene and carotene than spring tomatoes. The nitrogen-peeled samples were canned without additives, with sodium chloride and with calcium chloride added and compared with samples peeled with boiling water. There was a decrease in the percentage of broken fruit in the canned tomatoes peeled by liquid nitrogen. Titratable acidity and °Brix were higher and pH was lower in these samples. Color of the homogenized canned product was not statistically different; however, the nitrogen-peeled tomatoes had a better visual color. The calcium chloride added-nitrogen-peeled samples possessed a higher degree of firmness than the comparably treated boiling-water-peeled samples, indicating that the nitrogen-peeled tomatoes utilized the added calcium to a greater extent in firming.     

Antioxidant activity in different fractions of tomatoes

The objective of this study was to determine the major antioxidants and antioxidant activity in different fractions (skin, seeds and pulp) of three tomato cultivars (Excell, Tradiro and Flavourine) grown under hydroponic conditions in a commercial greenhouse in New Zealand. It was found that the skin fraction of all cultivars had significantly (p < 0.05) higher levels of total phenolics, total flavonoids, lycopene, ascorbic acid and antioxidant activity (both in hydrophilic and lipophilic extracts as measured by the ABTS assay) compared to their pulp and seed fractions. The amount of antioxidants in each fraction was calculated on the basis of their actual fresh weights in whole tomato and it was found that the skin and seeds of the three cultivars on average contributed 53% to the total phenolics, 52% to the total flavonoids, 48% to the total lycopene, 43% to the total ascorbic acid and 52% to the total antioxidant activity present in tomatoes. These results show that removal of skin and seeds of tomato during home cooking and processing results in a significant loss of all the major antioxidants. Therefore, it is important to consume tomatoes along with their skin and seeds, in order to attain maximum health benefits.     

Numerical Simulation of Variable Water Diffusivity during Drying of Peeled and Unpeeled Tomato

Abstract: A mathematical model was formulated for the estimation, in conjunction with experimental measurements, of water diffusivity parameters during convective drying of peeled and unpeeled tomatoes. Fick's 2nd law of diffusion was solved numerically for a sphere, by explicit finite differences, considering shrinkage effect, variable diffusivity, and constant boundary conditions. Experiments were performed in a laboratory tunnel dryer. The equivalent radius of tomato decreased by 50% until the end of the process, which explains the necessity for shrinkage inclusion in the mass transfer model. The mean estimated diffusivities varied between 2.03 × 10^?10 and 15.1 × 10^?10 m²/s for peeled tomatoes and 0.59 × 10^?10 and 15.2 × 10^?10 m²/s for unpeeled tomatoes. The estimated water diffusivities and their variation with the tested drying temperatures (45, 55, and 65 °C) provide an insight of peeling effect during air‐drying. Peeling was beneficial since yielded greater drying rates and shortened significantly drying times, thus saving energy during drying. In all the studied cases, good agreement was found between experimental and predicted drying curves (≥ 0.99, mean relative deviation [MRD]≤ 0.12, and root mean square error [RMSE]≤ 0.03). In overall, the proposed methodology provides a reliable and easy estimation of temperature and moisture‐dependent mass transfer properties and drying simulation of shrinkable food products such as tomato. Practical Application: Water diffusivity is a food property, difficult in estimation but essential in drying processing optimization. This property was estimated as a function of moisture content and drying temperature employing a numerical simulation procedure. The peeling effect was also studied and found beneficial for lower temperature drying (<55 °C) which is useful in the energy optimization of the drying process as well as the retention of the end‐product quality.     

Understanding Tomato Peelability

Approximately 75% of all tomatoes in the United States are consumed as processed and 25% as fresh. One of the first steps during processing involves removal of the peel and, unfortunately, more than 25% of the fruits (as measured by total weight) can be lost due to overpeeling. Additionally, conventional peeling applications have a negative environmental impact. Given the great potential economic benefits, many scientists have conducted research to attempt optimizing or predicting peeling performance when processing tomatoes. The literature regarding tomato peelability is contradictory in many cases; and several topics have been subject to ample debate over the years. Divergent conclusions are probably not due to faulty investigations, but rather to the extreme variability found among tomato cultivars, the effect of growing seasons, and maybe even the effect of climatic conditions on the day of harvest or during transportation to the processing plants. This review provides an in‐depth background needed for a better understanding of tomato physiology, maturation, and composition, as these could possibly influence the ease of peeling or “peelability.” The research studies directly involved with peeling tomatoes and predicting peelability are discussed in this paper as well. Different peeling methods, peeling grading scales, and fruit tagging procedures are presented, as well as experiments evaluating the effect that fruit defects, maturity, growing conditions, and other factors can have on the ease of peeling. Novel approaches for peelability prediction by means of spectroscopic and magnetic resonance technology are also discussed in this review.     

Quality and Nutritional Status of Fresh-Cut Tomato as Affected by Spraying of Delactosed Whey Permeate Compared to Industrial Washing Treatment

The aim of this study was to examine the applicability of delactosed whey permeate (DWP) treatment on preserving the quality and antioxidant attributes of fresh-cut tomato. Tomatoes were treated with 3% DWP by dipping, spraying and a combination of both, stored at 4?°C for 10?days and compared with the industrial standard, chlorine. The combination of dipping and spraying of DWP showed the best results for all the markers tested. The combined treatment of dipping and spraying of DWP significantly lowered total counts (??1.0 log cfu/g), yeast and moulds (??1.2 log cfu/g), inhibited the loss of firmness (25%) and reduced POD activity (15%) of the tomato slices after 10?days compared to the chlorine treatment. Moreover, DWP-treated tomatoes maintained significantly (p?<?0.05) higher levels of vitamin C, total phenols and antioxidant activity (DPPH) than the chlorine-treated samples during storage. Sensory scores confirmed that DWP-treated tomatoes retained better aroma and texture. Also, the appearance and overall acceptability were higher than chlorine-treated tomatoes. Thus DWP treatment has potential to extend the shelf life of fresh-cut tomatoes.